The hypothesis that progenitor cells in the bone marrow (bone marrow derived liver progenitor cells, BMLP) can give rise to liver cells will be formally tested in vivo and in vitro. In specific Aim 1 we propose a series of six experiments in which bone marrow or liver derived stem cells are transplanted into recipients. These experiments will define: 1) The conditions which activate BMLPs in the donor. 2) The conditions which may increase the ability of the recipient to accept and to nurture BMLPs. 3) The relationship of BMLPs to liver derived liver progenitor cells. 4) The ability of an hepatoblast cell line to give rise to bone marrow precursors. 5) Optimal markers for detection of transplanted cells. Donor mice will include normal male, lacZ male and EGFP male mice. Donor cells in irradiated female recipients will be detected by the presence of Y-chromosome and B-gal or EGFP. In specific Aim 2, bone marrow or blood cells will be cultured, using conditions known to be selective for hepatoblasts, to determine if colonies with hepatocyte phenotype can be produced. In both Specific Aim 1 and specific Aim 2, bone marrow and blood cells will be isolated from both normal mice and mice following partial hepatectomy or after cocaine induced periportal injury, experimental models to induce hepatocyte proliferation or periportal liver stem cell proliferation, respectively. These manipulations are known to induce growth factors for hepatocytes and liver stem cells and may encourage liver determination of HSCs. In addition, attempts will be made to isolate "pre-progenitor" cells from the bone marrow or liver that may have multilinege potential. In vitro colonies will be identified morphologically and passaged for analysis of differentiation potential after transplantation, phenotypic expression, growth properties, response to differentiating stimuli, and ultrastructure. Similar in vitro studies will be done on human bone marrow and blood using reserve cell preparations from the bone marrow transplant laboratory, which would otherwise be discarded. If this project is successful, it would overcome a major hurdle in the possible use of hepatic stem cells for treatment of liver failure or ex vivo gene therapy.